In the IBM history series by Pugh et al, they said IBM converted
> punched cards to paper tape for transmission in the 1940s. My guess
> is that that particular transmission used telegraph TTY lines (not
> voice) of either AT&T or Western Union. Recall that AT&T maintained
> telegraph long distance lines as part of carrier long distance
> circuits. Because of the low bandwidth, a telegraph channel could be
> carried on the low end of a carrier channel. Accordingly, no
> modulation was required and thus no modem needed.
> It was also said IBM limited development in this area to avoid
> annoying AT&T who was IBM's best customer.
> However, in the 1950s, IBM developed card-to-card directly without
> paper tape and "over AT&T lines". Modems were developed to take good
> advtg of the available bandwidth (about 1200 baud). Undoubtedly the
> equipment and implementation was developed in close cooperation with > AT&T.
> I was wondering if the modems in that application were supplied by IBM
> (who appears to have developed the technology) or by AT&T. My
> understanding that AT&T's "Dataset" modem-telephones didn't come out > until the 1960s.
> Comments by anyone familiar with pre-1960 data communications would be
> greatly appreciated.
Here is a picture of a 1958 AT&T modem (not sure if this is the first commercial modem, the Bell 103. If so it was 300 baud):
formatting link
Brad H